It's never a good sign when the funniest line in your romantic comedy is, "Did you visit the Holocaust museum?"

It’s never a good sign when the funniest line in your romantic comedy is, “Did you visit the Holocaust museum?” and has nothing to do with the rest of the movie. Such is the case with “What’s Your Number?,” a draggy, generally laugh-free outing that wastes a perfectly good Anna Faris, here playing a spacy sexpot who decides, after having slept with 20 different guys, that it’s probably time to settle down. With Chris Evans cast as an all-too-obvious Mr. Right, this inane I’ll-never-be-slutty-again farce should post OK theatrical and homevid numbers for Fox.

Ditched by her latest fling (Zachary Quinto) about five minutes after the opening credits, Ally Darling (Faris) is a boozy Boston blonde whose dating standards have plunged lower than her neckline. When she reads a magazine article about how the average American woman has 10.5 lovers over her lifetime, Ally realizes she’s slept with nearly twice that number and is in danger of making herself unmarriageable. That she’s recently lost her job and has no apparent interests beyond making clay-figurine dioramas doesn’t improve her prospects.

Resolving to stop fooling around and find a husband, Ally decides to look up her ex-boyfriends, one by one, in hopes of rekindling an old flame without raising her number to 21. Helping her with some detective work is her neighbor Colin (Evans), a laid-back guitarist and serial womanizer who’s clearly hot for Ally himself, though she’s wary of hooking up with someone even more whorish than she is.

So begins a series of mirthless wild-goose chases as Colin helps Ally stalk her exes across the country. One of them (Chris Pratt) seems to have shed a few hundred pounds and is now engaged to a sexy engineer; another (Anthony Mackie) asks her to marry him for the least romantic possible reasons. She steers clear of the more nightmarish suitors, who are relegated to flashbacks.

Ally’s clearly wasting her time, and the viewer may come to feel likewise. Unable to build or sustain comic situations, Gabrielle Allan and Jennifer Crittenden’s script (adapted from Karyn Bosnak’s novel “20 Times a Lady”) resorts to jokes so random and context-free they almost qualify as non sequiturs, cueing viewers to laugh when a bit player turns out to be a compulsive finger-sniffer or when Ally’s hair catches fire for no reason.

Less vulgar and over-the-top than some of the year’s other R-rated comedies, “Number” riffs on the pitfalls of promiscuity en route to a predictably safe, sweet, pro-commitment happy ending. Viewers will get their fill of coy near-nudity and genital-centric one-liners, but none of the sophistication or honesty about gender-based double standards they might reasonably expect from such a scenario. Pic does bear a vague resemblance to recent summer hit “Bridesmaids” in the way it uses an upcoming wedding (that of Ally’s sister, nicely played by Ari Graynor) to zero in on a single gal’s early-midlife funk, but its portrait of distaff distress is nowhere near as insightful or funny.

A superior comic actress whose talents have been better showcased elsewhere, Faris works little of her usual magic here, largely because the film essentially shares Ally’s dim opinion of herself. There’s no secret-weapon intelligence or killer timing behind Faris’ ditzy veneer this time; she really is just playing a dumb blonde who can’t hold her liquor. Evans’ nice smile and nicer muscles get the job done, and Blythe Danner and Ed Begley Jr. submit OK turns as Ally’s divorced parents.

Glossily helmed by Mark Mylod (“Ali G Indahouse”) and crammed with tiresome pop-slathered montages, “Number” also teems with references to Facebook and Twitter that are meant to show how up-to-the-minute the film is, but will have the effect of dating it instantly.

What's Your Number?

Production

A 20th Century Fox release of a Regency Enterprises presentation of a New Regency/Contrafilm production. Produced by Beau Flynn, Tripp Vinson. Executive producers, Arnon Milchan, Anna Faris, Nan Morales. Directed by Mark Mylod. Screenplay, Gabrielle Allan, Jennifer Crittenden, based on the book "20 Times a Lady" by Karyn Bosnak.